Variable resistor constructions



Aug. 28, 1962 M. E. BOURNS ETAL 3,051,921

VARIABLE RESISTOR GONSTRUCTIONS Original Filed July 26, 1954 a?? 9o c |00 feo ..99 85 ///7/ .rau

7' 9o FIG.9 '25 qloal 82 W) 92 /|I// /I//// United States Patent O 3,051,921 VARIABLE RESISTR CGNTRUCTIUNS Marlan E. Bottins, Wiibnr T. I-Iardison, and Warren i).

Hulbert, Riverside, Calif.; said Hardison and Hulbert assignors to Bonrns, Inc., a corporation of Caiifornia Original application July 26, 1954, Ser. No. 445,534, now

Patent No. 2,8S2,37, dated Apr. 14, 1959. Divided and this application Mar. 2, 1959, Ser. No. 809,331

6 Claims. (Cl. 33--1S1D The present invention is concerned with new and improved variable resistor constructions, and is a division of our co-pending application, Serial No. 445,534, tiled Iuly 26, 1954, now Patent No. 2,882,375, for Variable Resistor Constructions. More specifically it is concerned with extremely small resistors, although, obviously many of the constructional details herein described are capable of being used on comparatively large electrical components of the class described. A broad object of the invention is to provide new and improved variable resistor constructions. A more specific object is to provide variable resistors which are comparatively cheap to construct, reliable in operation, and which can be manufactured in very small size. Further areas or objects of this invention will be apparent from the remainder of this specification.

This invention may be summarized as being concerned with variable resistors each having an elongated housing, preferably formed of `an insulating material within which there is disposed at least one resistance member, another electrically conductive member which may be a resistance member, a metallic contact member, and means for moving this contact member with respect to the resistance member and the electrically conductive member, and from which housing there project appropriate electrical terminal members and said means for moving the metallic contact member. The invention is more fully summarized by the appended claims. Further details of the invention are best apparent `from the balance of this specification, the appended claims, and the accompanying drawings, in which:

FIGURE l is a top view of a resistor of the invention;

FIGURE 2 is a partial cross-sectional view taken at line 2-2 of FIGURE l;

FiGURE 3 is a cross-sectional View taken at line 3 3 of FIGURE l;

FIGURE 4 is a View similar to F'IGURE 2 of a modiied construction of the invention;

FIGURE 5 is a cross-sectional view taken at line 5-5 of FIGURE 4;

FIGURE 6 is a view similar to FIGURE 2 of a second modiiied construction of the invention;

FIGURE 7 is a cross-sectional view taken at line 7-7 of FlGURE 6;

FIGURE 8 is an isometric view of a resistance member which may be employed with the invention; and

FIGURE 9 is a View similar to FIGURE 3 of a third modified construction of the invention.

The various items shown in the drawings have been drawn so as to best illustrate particular features as will be more fully described. For this reason the majority of parts shown in the various figures are not necessarily to the scale of proposed commercial units embodying the constructions shown.

In FIGURES l, 2 and 3 of the drawings there is shown a variable resistor construction 1d which includes bilaterally symmetrical shell-like sections 11 formed of an insulating material such as a lled phenolic resin, which sections are secured together by rivets 12 so as to form a complete housing within which there is disposed a conductive metallic member 14 and a cylinder 15 provided with an external resistance iilm 16. Both the member 14 and the cylinder 15 are held in position between ICC the sections 11 by means of insulating ledges 17 extending along the sides 1S of the Sections 11 between the ends 19 of these sections. Electrical connections to the member 14 and the cylinder 15 are made `by means of conductive terminals 20 which are each formed so as to have a shank section 21 projecting through the ends 19 of the sections 11. The terminals 20 include upstanding center portions 22 positioned so as to lie against the internal surfaces of the ends 19 and bent over contact sections 23 which are designed to engage either the member 14 or the extremities of the cylinder 15 with a spring action so as to at all times be in electrical contact with this member 14 and the film 16.

A threaded metallic shaft 24 extending beyond the sections 11 is held within semi-cylindrical depressions 25 in the ends 19 of the sections 11 so as to project generally parallel to the ledges 17, the member 14 and the cylinder 15. Adjacent to the exterior of these sections y11 the shaft 24 is provided with slots 26 which are engaged by insulating caps 27 of a resin such as indicated above or like material formed so as to encase the portions of shaft 24 projecting from the ends 19. These caps 27 are each provided with slots 2S designed to be engaged with a screw driver so `that the shaft 24 can be turned.

A contact member 30 formed of a single strip of metal bent so as to have a lirst side 31, a second side 32 attached to said first side 31 by a rst apex 33 and manufactured so as to have aligned apertures 34 and 35 within the sides 31 and 32 respectively, is placed between the sections 11 with the shaft projecting through the apertures 34 and 35. The exact shape of these apertures may be varied within wide limits. Preferably however, they are of generally oval shape so that as the sides 31 and 32 are pressed toward one another the shaft 24 may be easily inserted through them and so that as these sides are released the edges of the metal strip at the openings vwill be brought into engagement with the shaft 24- because of the inherent resiliency of the material from which the contact member 31D is formed. Preferably at least one of the apertures 34 or 35 is formed so as to have edges which are designed in a conventional manner to engage the threads upon the shaft 24 so that as the shaft is turned the contact member 319 is moved upon it. The portions of the shaft 24 immediately adjacent to the sections 1I are preferably not threaded so that the contact member 30 Will upon continued rotation of the shaft in either direction move substantially off the threaded portion of the shaft and engage the ends y19, causing this member to temporarily disengage the threads on the shaft 24.

The contact member 3G includes an end 36 attached v to the second side 32 by means of a second apex 37. This apex y37 is designed to ride against the surface of the iilm on cylinder 15 as the shaft 24 is turned. During such motion the parts of the contact member 30 adjacent to the ledges 17 engage these edges, preventing rotation of the member 30. The contact member 30 also includes an attached member 38 projecting from either of said sides 31 or 32 beyond said first apex 33. This member 3S includes an upturned end 39 attached to it yby means of a third apex 4t). This third apex 4i) is designed to engage the member 14 so as to at all times be in electrical contact with it. It is considered obvious from the drawings that the entire contact member 30 may be conveniently manufactured from a single piece of metal by a simple stamping operation and that the apexes 37 and 40 are designed to be held against the member 14 and the film 16 as indicated with a spring-like action resulting from the inherent resiliency of the material from which the contact member 30 is manufactured.

The assembly of the variable resistor construction 1d is exceedingly simple, and marks one of the major advantages of this specific construction. In manufacturing it one of the sections lll is placed upon a table or other supporting surafce and the various parts specifically indicated in the preceding discussion are merely laid in position upon it. The terminals Ztl are inserted with slots l2 formed in the section lll so as to be biased against the conductive member with which they make contact before the other of the sections Il is applied to the unit. Similarly the contact member 30 is placed in substantially its nal position, and then as the other section Il is positioned over the section Il. upon the supporting surface and all of the various parts are trapped in assembled relation. The construction i6 is completed by heading over the rivets l2 in an obvious manner. If desired, other equivalent fastening means such as an adhesive can be employed instead of these rivets.

The modified construction 56 shown in FIGURES 4 and is composed of two shell-like sections 5l and 52; composed of an insulating material which are designed to fit together in substantially the same manner as the sections ll. The section 5l is provided with a substantially rectangular internal cavity 53, the bottom of which is filled with a resistance composition 54 which may, if desired, be molded in situ, or may, if desired, be inserted within the section 5l after this section has been formed. Electrical contact can be made to this resistance composition 54 by means of metallic terminals 55 including exterior portions 56 designed to tit against the exterior surface S7 of the section 5l, attached center portions S8 designed to t witln'n notches 59 formed within the section 5l, attached internal portions 6@ designed to engage the internal surface of the cavity 53 so as to form what in effect may be considered a spring clip engaging the section 5l and extending over the top thereof. The portion 6l) is connected to an end 6I of bent configuration as illustrated in FIGURE 5 which is designed to engage the resistance composition 54 with a spring-like action so as to establish electrical contact therewith.

The section S2 is also provided with a substantially rectangular internal cavity 63 which, if desired, may be used to contain a non-conductive cylinder 64 provided with an external resistance coating 67. This cylinder 64 is designed to be held in place by means of metallic terminals 65 including exterior portions 66 which are intended to lit against the exterior surface of the section 5I. These terminals 65 also includes center portions 68 which are designed to fit within notches 69 formed within the sections 52 and attached internal portions 62 lying against the surface of the internal cavity 63. The terminals 65 each contain an end section 7@ bent the general shape of the cylinder 64. As is illustrated in FIGURE 5 these sections 76 are designed to engage the cylinder 64 with a spring-like action forming electrical contact with the resistance coating 67. If desired, the ends 7@ may be provided with terminal extremities 71 which are designed to engage a surface of the cavity 63 remote from the surface of this cavity engaged by the internal portions 62 so as to firmly hold the terminals 65 in position within the section 52 by a spring-like action.

Within the construction 56 there is provided a metallic contact member '75 of substantially the same construction as the contact member 3i) shown in FIGURES 2 and 3 of the drawing. Because of the similarity of constructional details between the two contact members like parts of each are designated by the same numerals. The contact member 75 is carried by an elongated shaft 76 formed of an insulating material so as to be threaded in the same manner as the shaft 24. This shaft 76 is designed to project from both ends of the construction 5t) through depressions 77 of substantially semi-circular configuration formed in the sections 5l and 52, and is designed to be held in place by collars 7S formed on the shaft 76 bearing against the surfaces of the cavities 53 and 63. With this specific construction the member 76 may be turned causing the appropriate parts on the contact member 75 to engage the resistance coating 67 and the resistance composition 5ft in the expected manner. When the iinal construction 56 is assembled the sections 5l and 52 are preferably secured together by an appropriate adhesive although other equivalent means may be used.

In FIGURES 6 and 7 of the drawing a second modified construction 86 of the invention comprising a shell-like section Sl of an insulatingr material defining together with a lid 32 of a transparent insulating material such as those marketed under the trademarks Lucite, Plexiglas, etc., a complete housing having an internal cavity 83 is shown. The lid S2 and the section til are normally secured together by an adhesive or other equivalent means. Within the section 8l there is provided a resistance composition S4 which may, like the composition 5d, be either positioned within the supporting section Sl or be molded in situ within this section. Terminal connections are made to the composition 34 by means of electrically conductive rivets 65 which are either molded within the section Sl or are inserted within apertures in this section after it has been formed. Each of the rivets S5 is secured in the obvious manner to small metal terminal tabs 66 positioned upon the outside section 8l.

Located within an aperture S7 formed within an end 3S of the section 3l so as to proiect from this end 3S into a. circular depressed cavity E66 formed within the other end 88 of the section Sl is a conductive shaft 96 which is threaded intermediate its ends and preferably has an unthreaded end portion engaging the cavity 166, this Unthreaded portion having a cross-sectional diameter equal to or slightly smaller than the minor diameter of the threaded portion of the shaft 9d, such that the contact lmember i655 may disengage the threaded portion of the shaft upon reaching the right-hand travel extremity, thereby preventing the breakage of the housing incident upon the turning of the shaft 9i) an excessive number of revolutions. rThe Contact member 65 is so constructed that spring pressure exerted by the end of the contact member E05 against the inside of the internal cavity 83 causes the spring to again engage the threaded portion of the shaft 90 when the shaft @il is turned in a reverse direction, causing the contact spring to move toward the left-hand end of the instrument. This shaft is secured in position by means of a tab ltl' formed integrally with the lid 82, projecting from this lid so as to engage a groove 16S formed Within the shaft 9i?. This shaft is also secured to a non-conductive cap 92 externally of the section till by means of one or more non-conductive pins 91; this cap 92 is provided with a slot 93 of the conventional type designed to receive a screw driver. Electrical contact is made to the shaft 90 by means of a metal terminal 95 including a portion 96 adapted to lie along the outside of the section 3l, a center section 97 designed to fit within a notch 98 within this section 8l and a portion 99 designed to t against the internal surface of the section 8l in such a manner that the entire terminal 95 is held in position with a spring or clip-like action. The portion 99 of the terminal 95 is provided with an end section I0@ which is normally biased by a spring-action, resulting from the inherent resiliency of the material from which the terminal 95 is manufactured, against a cyilndrical section ltil of the shaft 90 so as to be in electrical contact with this shaft as it is turned.

The shaft 90 carries a contact member 165 of substantially the same construction as the contact member 30 except for the omission of the attached member 33 projecting from the contact member 36. Because of the simi larity of construction details the same numbers are used to designate parts of the contact member 165 as are used to designate equivalent parts of the contact member 30.

One important feature 'of the specic construction shown in FIGURES 6 and 7 of the drawings relates to the fact that the position of the contact member within the construction 80 is readily visible through the lid 82. If desired, various markings may be applied to this lid 82, which correspond to the position of the apex 33 of the contact member 105 or to other parts of the contact member so that at all times it is possible to accurately determine the position of the contact member within the construction 80.

In FIGURE 9 of the drawings there is shown a variable resistor construction 110 which differs from construction 80 shown in FIGURES 6 and 7 in only several minor regards. This specific construction 116 involves the use of a non-conductive lid 111 to which there is secured either by means of an adhesive or by metallizing techniques a thin layer of a conductive metal 112. This lid is used to cover a shell-like section 113 formed of an insulating material so as to define an internal cavity, and is secured to this shell-like section by means of an adhesive or like means in such a manner that the layer 112 faces this internal cavity 114, This cavi-ty is of such dimension as to easily hold a shaft 116 which carries a contact member (not shown). Both the shaft and the contact member employed with this embodiment of the invention are substantially identical to the equivalent members employed in the construction 80 illustrated in FIGURES 6 and 7.

The contact member employed in the embodiment of FIGURE 9 is adapted to move against a wound resistance unit of a type specifically illustrated in FIGURE 8 of the drawings as including a generally oval cross-sectioned elongated body 11S of lan insulating material around which there are positioned a number of turns 119 of a resistance wire. These turns 119 `are of the conventional category employed in wire-wound resistors and are connected at one end of the body 118 to `a large mass or group of turns 120 of the same resistance wire. The unit 115 is designed so that the contact member employed is intended to make contact with the turns 119. With this construction the turns 120 provide a large resistance value coupled with what in effect amounts to a very tine adjustment of the resistance by the use of the turns 119.

The resistance unit 11S employed in the construction 110 is normally held in position by means of spring clips 121 having opposed bowed sides 122 positioned against opposed sides of the cavity 114 in such a manner that these sides engage the resistance unit 11S when this unit is inserted within the cavity 114 so as to hold it firmly in place. The spring clips used are disposed at opposite ends of the cavity 114 in such a manner that they make contact with the portions of the windings or turns 119 and 120 farthest removed from one another. Both of these spring clips 121 are provided with bottom walls 123 co-nnected to the sides 122. These bottom walls 123 are so designed as to pass together outwardly through an appropriate aperture (not shown) Within the section 113 in a conventional manner.

With the construction 110 electrical contact is made to the layer 112 -by means of a terminal 125 whic embedded within the walls of the section 113 as indicated in FIGURE 9 of the drawing so as to project from both the bottom of this section adjacent to the spring clips 121 and so as to project from the walls of the section 113 into the internal cavity 114 adjacent to the top of this cavity. There the terminal 125 is provided with an end 126 which is adapted to be held against the layer 112 by spring tension so as to be in electrical contact with this layer.

The various variable resistor constructions illustrated in the accompanying drawings and described in the aforegoing discussion constitute a very distinct advance in the art in that they are all extremely reliable in operation and yet are extremely simple to easily and cheaply produce on a production line basis. Further, many of the operative parts of the resistor constructions described, such as, for example, the contact members indicated, may be easily and cheaply fabricated and are exceedingly reliable for use with other constructions besides those specically indicated. Inasmuch as all of the resistors shown employ housings which are non-conductive, these resistors are immune from shorting troubles which have plagued 5 other related resistor constructions. The resistors herein described are specifically intended to be manufactured having `a cross-section size of approximately ls by 1A inch.

Those skilled in the art will realize that a number of minor modifications may be made within the precise constructional details indicated without departing from the scope `of this invention. All such modifications of this category which are within the skill of the art are to be considered as part of this invention.

We claim:

l. A new and improved variable resistor construction including: an elongate insulative housing having sides and opposed ends; a resistance member disposed within said housing adjacent to one of said sides; an electrically conductive screw-threaded shaft positioned principally within said housing and having an end disposed so as to be accessible from the outside of at least one of the ends of the housing; a reversely bent metallic conductivespring contact member having opposed apertured portions, disposed within said housing in engagement with said shaft and with lthe shaft extending through the apertures so as to be moved by rotation of the shaft, the contact member being in electrical contact with said resistance member; a spring metal terminal strip extending through and embedded in one side `of said housing adjacent an end thereof, said terminal strip extending transversely of said housing and resiliently bearing against the side of said shaft so as to make electrical Contact therewith; and terminal means each attached to `a respective end portion of said resistance member and projecting through said housing.

2. A variable resistor comprising: an elongate housing formed of an electrically non-conductive material and having sides and opposed ends; an elongate resistance element disposed within said housing adjacent one of said sides; an electrically conductive screw-threaded shaft rotatably supported by said housing parallel to said resistance element, one end of said shaft projecting outwardly through an aperture in one of said ends of said housing; a head of non-conductive material iixed to said one end of said shaft, said head being formed to receive an adjusting tool; a reversely bent spring contact member having opposed apertures through which said shaft extends and Which member .is operatively engaged at two spaced-apart locations by the thread of said lead--screw so as to be moved thereby along the shaft, said contact member wiping on said resistance element and making an electrical connection with said shaft; and a spring metal terminal strip extending through and embedded in one side of said housing, said terminal strip extending transversely of said housing and resiliently bearing against the side of said shaft so as to make electrical contact therewith, and other terminal means connected to said resistance element.

3. A variable resistor of the leads screw-actuated type, said resistor comprising: h

first means, including an elongate housing means presenting an electrically insulative exterior surface and opposed end-Wall means interconnected by elongate longitudinal Walls;

second means, comprising elongate resistance element means secured in said housing, and terminal means for said element extending to the exterior of said housing;

third means, comprising elongate electrically conductive screw-threaded shaft means journaled at opposite ends thereof in said opposed end-wall means, said third means including electrically insulative means engaging one end of said shaft and constructed and arranged for rotating said shaft;

fourth means, comprising essentially a conductive spring contact having two portions encircling said shaft and engaging the latter to be driven by the shaft upon rotation of the shaft, said contact being constructed 7 d and arranged to wipe said resistance element and electrically interconnect the contact and said shaft;

and fifth means, comprising a spring terminal element embedded in and extending through a wall of said housing means, said terminal element having a resilient extension in said housing conductively contacting said shaft means.

4. A variable resistor of the type wherein a linearly movable conductive spring-contact is moved longitudinally along an extent of an elongate terminated resistance element by rotation of a screw-threaded shaft that is arranged substantially parallel to the resistance element and the resistance element is disposed in a molded insulative housing, characterized by a resilient electrically conductive terminal element extending outwardly from and embedded in and supported by the housing and pressing against a portion of the shaft, whereby the resistance element is electrically connected to the terminal by way of the spring-contact and the shaft.

5. A variable resistor according to claim 4, further characterized by the screw-threaded shaft having a threadless portion adjacent one end thereof, upon which threadless portion the conductive terminal presses.

6. A variable resistor according to claim 4, further characterized by the conductive spring-contact having integral opposed apertured limbs disposed at an acute angle each to the other and by the screw-threaded shaft extending through the apertures in the limbs of the Contact, and further characterized by the screw-threaded shaft having threadless opposite end-portions separated by a threaded portion, whereby upon continued rotation of the shaft in either direction of rotation the contact moves susbtantially ot the threaded portion of the shaft and onto a threadless portion to limit linear motion of the contact along the resistance element.

References Cited in the tile of this patent UNTTED STATES PATENTS 1,668,117 Kent May 1, 1928 1,673,443 Crosley June 12, 1928 1,955,906 Crouse Apr. 24, 1934 2,687,463 Riley Aug. 24, 1954 2,745,054 Leyenberger May 8, 1956 2,912,663 Van Allen Nov. 10, 1959 2,932,808 Bourns et al Apr. 12, 1960 

